<div class="htmlview paragraph">A brief outline of the elementary principles of the operation of jump-spark ignition systems is given preliminarily to the discussion of the advantages of battery-type systems, and four vital elements in a jump-spark ignition system are stated. A diagram is shown and explained of an hydraulic analogy, followed by a discussion of oscillating voltage and oscillograms of what occurs in the primary circuit of an ignition system when the secondary is disconnected.</div> <div class="htmlview paragraph">The subjects of spark-plug gaps and current values receive considerable attention and similar treatment is accorded magneto speeds and spark polarity, numerous oscillograms accompanying the text. The effects of magneto and of battery ignition on engine power are stated and commented upon and this is followed by a lengthy comparison of battery and magneto ignition, illustrated with charts. The author reports satisfactory performances of battery ignition during automobile speed-contests, and airplane altitude and trans-Atlantic flights, which prove that it will function and give satisfactory results under the most severe conditions of service.</div>